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Media Server / SLP Duplication Question

Created: 22 Jan 2013 • Updated: 02 Apr 2013 | 12 comments
This issue has been solved. See solution.

I'm curious about how NetBackup decides which media servers should be used for SLP duplications.

 

We have 2 Data Domains which we back up to, with a total of 4 media servers; these servers are then grouped in load balanced pairs. Generally our policies are set up so that one pair writes backups to one Data Domain while the other pair deal with the backups for the other Data Domain. However, all 4 media servers can access both Data Domains.

 

Looking at many of our SLP duplication jobs, the "Media server" listed in the detailed status is something along the lines of:

 

"exampleserver1 -> exampleserver2" (with each server being from a different pair as described above)

 

However, I have noticed that when the environment is busy overnight, any running SLP duplications often use the same server to read and write the image (e.g. "exampleserver2 -> exampleserver2"). Is this simply because the other servers are busier so NetBackup doesn't assign two different media servers for the duplication job?

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RamNagalla's picture

hi,

its because of the Network Optimized Duplication feature.

see the highlited once below 

 

 

New Network Optimized Duplication feature
NetBackup creates backup copies by duplicating the backup image from the source media to the destination media. In the following situations, NetBackup must select a media server selection for the duplication destination:
 If the duplication destination is a storage unit group
 If the duplication destination is a storage unit with shared drives that are accessible by multiple media servers.
 If the duplication source or destination is a disk storage unit configured to be accessible from multiple media servers.
In previous releases, NetBackup did not automatically attempt to use the same media server for both the source and the duplication destinations. To ensure that the same media server was used, the administrator had to explicitly target the storage units that were configured to use specific media servers.
 
In NetBackup 6.5.4 this behavior remains the default but it can be changed by using the following command:
 
nbemmcmd -changesetting -common_server_for_dup <default|preferred|required> -servername master server name
 
Select from the following options:
 
default – the default option (default) instructs NetBackup to try to match the destination media server with the source media server. Using the default option, NetBackup does not perform an exhaustive search for the source image. If the media server is busy or unavailable, NetBackup uses a different media server.
 
preferred – The preferred option instructs NetBackup to search all matching media server selections for the source. The difference between the preferred setting and the default setting is most evident when the source can be read from multiple media servers, as with Shared Disk. Each media server is examined for the source destination. And for each media server, NetBackup attempts to find available storage units for the destination on the same media server. If all of the storage units that match the media server are busy, NetBackup attempts to select storage units on a different media server.
 
required – the required option instructs NetBackup to search all media server selections for the matching source. Similar to the preferred setting, NetBackup never selects a non-common media server if there is a chance of obtaining a common media server. For example, if the storage units on a common media server are busy, NetBackup waits if the required setting is indicated. Rather than fail, NetBackup allocates source and destination on different media servers.
 
 
 

 

CRZ's picture

I think it's this one :)

Best practices for configuring NetBackup with Storage Lifecycle Policies
  http://symantec.com/docs/TECH75047


bit.ly/76LBN | APPLBN | 75LBN

Shaun Taylor's picture

Thank you for the replies - that's some useful info. So it's preferable for the same media server to be used?

Does NetBackup have to involve the media server that wrote the original backup when it duplicates? As I explained, all 4 of my media servers can access both Data Domains so even if the original backup server is busy, could NetBackup not use another idle media server to read and write for the duplication? Or is this what using the required option would achieve?

Looking at the default option of Network Optimized Duplication feature ("If the media server is busy or unavailable, NetBackup uses a different media server" in particular), I seem to be getting the opposite for many of my duplications. I checked some SLP duplications that ran when the environment was either very quiet or had no jobs running at all, and it still used 2 different media servers for the duplication in most cases. Very confusing! Or have I misunderstood the default option?

If it is preferable for the same media server to be used for read and write (and a delay in resource allocation isn't a problem for me), should I consider running the "nbemmcmd -changesetting -common_server_for_dup" command to use the preferred or required option?

RamNagalla's picture

hi,

as you are saying "checked some SLP duplications that ran when the environment was either very quiet or had no jobs running at all, and it still used 2 different media servers for the duplication in most cases."

by any chage alternate read server is selected  in SLP?

please use Preferred option and see how its works.

nbemmcmd -changesetting -common_server_for_dup preferred -servername master server name

Shaun Taylor's picture

I've double checked and we definitely don't have an alternate read server selected on any of our SLPs.

Just out of interest, why do you recommend the preferred option over the required option? Also, can anyone advise on my other questions from above?

Does NetBackup have to involve the media server that wrote the original backup when it duplicates? As I explained, all 4 of my media servers can access both Data Domains so even if the original backup server is busy, could NetBackup not use another idle media server to read and write for the duplication? Or is this what using the preferred/required option would achieve?

Thanks for your help so far.

Marianne's picture

Have a look at this TN: http://www.symantec.com/docs/TECH87200

DOCUMENTATION: Restores and duplications from OpenStorage backup need not use the same media server that wrote the backup.

Solution: 

1. In most cases creating this touch file on the master server will force Open storage backups to use the media server that did the backup.

   /usr/openv/netbackup/db/config/USE_BACKUP_MEDIA_SERVER_FOR_RESTORE
 

Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links

Shaun Taylor's picture

Thanks for the response Marianne - I'll take a look.

Mark_Solutions's picture

If the duplications / replications are using Opt Dup then it doesn't really matter which media server it uses as the actual process will go from de-dupe appliance to de-dupe appliance, the media server is just an incidental part of the process as it doesn't actually do anything

In general when you setup a Storage Server then in the credentials secton you have all media servers included within it as having access to it (first tab labelled Media Servers).

You find that if all are selected it will use any to do replications

The -required option is about the only way to prevent that happening in my experience other than unchecking the other media servers in this credentials section

Authorised Symantec Consultant

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SOLUTION
Shaun Taylor's picture

Ok, that's good to know. With regards to the media server not doing anything during an optimised duplication, I'm guessing it's only involved as part of the initiation of the job if it isn't involved in moving any data?

All of our media servers are listed for each storage server, exactly as you described. From the above, I'm still unsure if it's actually preferable for one media server to do both reading and writing for a duplication - although I'm guessing this is irrelevant for optimised duplication?

How can I confirm if we're using optimised duplication? DD Boost is licensed and enabled on the Data Domains and we're using v2.5.0.3 of the OST plugin on our media servers. This is actually something else on my list of things to look into and address in our environment!

Mark_Solutions's picture

I believe DD Boost  and DD in general is supported for OPT DUP - so data will go from DD to DD - all part of the OST-Plugin

Authorised Symantec Consultant

Don't forget to "Mark as Solution" if someones advice has solved your issue - and please bring back the Thumbs Up!!.

Shaun Taylor's picture

Thanks for the help everyone - I eventually found that OST Opt Dup wasn't being used in our environment due to our use of Storage Unit Groups. After checking with Symantec support, I restructured our DD Storage Units and SLPs and confirmed that Opt Dup is now being used.